The long term objective of the proposed research is to understand the mechanism by which RNA tumor viruses control the expression of their own genomes and influence the expression of genes in their host cells. Specific aims include studies of the biochemistry of retroviral DNA integration and identification and analysis of viral genomic sequences that control polyprotein and RNA processing. The avian sarcoma/leukosis viruses (ASLV) serve as the primary model systems. However, comparative studies with human immunodeficiency virus (HIV) are also planned. For studies of integration, experimental strategies include analysis of the relevant biochemical activities of proteins isolated from viral particles and produced in heterologous systems through recombinant DNA techniques. The heterologous systems will be exploited for their ability to provide large amounts of mature, active proteins and functional gene fragments that can be subjected to site-directed mutagenesis. A variety of DNA substrates containing putative viral integration sites will be tested in vivo using sensitive genetic assays to detect recombination events and to evaluate the investigated in vitro systems, which include cell extracts and virus- infected and/or purified protein and nucleic components. The protein processing studies will benefit from our growing knowledge of the biochemistry and three-dimensional structure of the retroviral protease. Mutants will be designed based on this knowledge and will be used to evaluate the contribution of protease activity to virion core morphogenesis. Genetic and biochemical approaches will also be used to identify and characterize viral RNA sequences involved in the control of RNA processing and to determine the mechanism of this control. For these studies, powerful genetic selection made possible by the availability of unique viral mutants will provide a special advantage. Results from this work will contribute to an understanding of the viral and cellular biochemical reactions that underlie retrovirus-induced cancer. In addition, the retroviruses represent a promising tool with which to enlarge our understanding of the general mechanisms involved in other instances of oncogenesis where genetic damage, gene amplifications or abnormal gene rearrangements and controls can trigger malignancy.